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Subject: [PATCH v1] virtio-balloon: always indicate S_DONE when migration fails
If something goes wrong during precopy, before stopping the VM, we will never send a S_DONE indication to the VM, resulting in the hinted pages not getting released to be used by the guest OS (e.g., Linux). Easy to reproduce: 1. Start migration (e.g., HMP "migrate -d 'exec:gzip -c > STATEFILE.gz'") 2. Cancel migration (e.g., HMP "migrate_cancel") 3. Oberve in the guest (e.g., cat /proc/meminfo) that there is basically no free memory left. While at it, add similar locking to virtio_balloon_free_page_done() as done in virtio_balloon_free_page_stop. Locking is still weird, but that has to be sorted out separately. There is nothing to do in the PRECOPY_NOTIFY_COMPLETE case. Add some comments regarding S_DONE handling. Fixes: c13c4153f76d ("virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT") Cc: Wei Wang <wei.w.wang@intel.com> Cc: Alexander Duyck <alexander.duyck@gmail.com> Signed-off-by: David Hildenbrand <david@redhat.com> --- hw/virtio/virtio-balloon.c | 24 ++++++++++++++++++++---- 1 file changed, 20 insertions(+), 4 deletions(-) diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c index 10507b2a43..13ba208694 100644 --- a/hw/virtio/virtio-balloon.c +++ b/hw/virtio/virtio-balloon.c @@ -628,8 +628,13 @@ static void virtio_balloon_free_page_done(VirtIOBalloon *s) { VirtIODevice *vdev = VIRTIO_DEVICE(s); - s->free_page_report_status = FREE_PAGE_REPORT_S_DONE; - virtio_notify_config(vdev); + if (s->free_page_report_status != FREE_PAGE_REPORT_S_DONE) { + /* See virtio_balloon_free_page_stop() */ + qemu_mutex_lock(&s->free_page_lock); + s->free_page_report_status = FREE_PAGE_REPORT_S_DONE; + qemu_mutex_unlock(&s->free_page_lock); + virtio_notify_config(vdev); + } } static int @@ -653,8 +658,6 @@ virtio_balloon_free_page_report_notify(NotifierWithReturn *n, void *data) case PRECOPY_NOTIFY_SETUP: precopy_enable_free_page_optimization(); break; - case PRECOPY_NOTIFY_COMPLETE: - case PRECOPY_NOTIFY_CLEANUP: case PRECOPY_NOTIFY_BEFORE_BITMAP_SYNC: virtio_balloon_free_page_stop(dev); break; @@ -662,9 +665,22 @@ virtio_balloon_free_page_report_notify(NotifierWithReturn *n, void *data) if (vdev->vm_running) { virtio_balloon_free_page_start(dev); } else { + /* + * Set S_DONE before migrating the vmstate, so the guest will reuse + * all hinted pages once running on the destination. + */ virtio_balloon_free_page_done(dev); } break; + case PRECOPY_NOTIFY_CLEANUP: + /* + * Especially, if something goes wrong during precopy or if migration + * is canceled, we have to properly communicate S_DONE to the VM. + */ + virtio_balloon_free_page_done(dev); + break; + case PRECOPY_NOTIFY_COMPLETE: + break; default: virtio_error(vdev, "%s: %d reason unknown", __func__, pnd->reason); } -- 2.26.2
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